43 research outputs found
Effect Of Alkali Ferrocyanides On Crystallisation Of Sodium Chloride: Preliminary results
No full textSodium chloride (NaCl) is one of the ubiquitous soluble salts in the environment and is responsible for weathering of building materials. The salt weathering is attributed to the stress developed from crystallisation of these salts in pores of the building materials, with supersaturation as the driving force. In the last years, researchers have successfully mitigated the damage associated with the crystallisa-tion of NaCl by the use of alkali-ferrocyanides (crystallisation inhibitors) in porous building materials. The observed mitigation of the damage has been attributed to lowering of the crystallisation pressure, possibly related to changes in the crystal habit and preferential crystallisation of the salt in the form of efflorescence instead of crypto-florescence. However, the effect of the inhibitor on the development of the so-called crystallisation pressure has not been studied in detail yet. In fact, direct measurement of this pressure is challenging and, until now, only a few experiments have been successful. In this research, an experimental setup has been developed to directly measure the crystallisation forces of NaCl and the effect of fer-rocyanide on these, while visualizing the crystallization process under a microscope. Some preliminary tests using this setup have been carried out: these consisted in monitoring force evolution from a drop of solution with and without the inhibitor confined between two glass plates.Heritage & TechnologyMaterials and Environmen
Characterization of forest canopy gaps caused by landslides using high density airborne laser scanning
No full textHigh density airborne laser scanning (HDALS) data has revolutionized the characterization of tree growth anomalies and complex vegetation attributes including forest canopy gaps (FCG). They pose significant impact to forest eco-logical and monitoring activities. This paper presents a new approach based on object oriented technique to extract FCG characteristics caused by complex landslides in the French Alps. With a substantial point density across the forested landslides (170 points m-2), the method had an overall detection rate of 81% and over-predicted the reference FCG. The statistical tests revealed significant differences of FCG in landslide and non-landslide zones at the 95% confidence level and supported the field evidences. The results are promising given the complex interaction between landslide processes and forest ecosystem in the area. This study highlights the potential contribution of HDALS data to a regional ecological hazard assessment and can be alternative tool to analyze disrupted vegetation induced by geomorphic processes in a complex environment
Towards a new salt crystallisation test: Comparison of salt contamination procedure
No full textThe RILEM TC 271-ASC is currently developing a new ageing test to assess theresistance of porous building materials to salt crystallisation. The new test consists of two phases: salt accumulation and damage propagation. This paper focuses on the salt accumulation phase; this phase should promote salt crystallisation close to the evaporative surface of the substrates (common situation onsite) without leading to salt efflorescence or damage. Damage should take place in the propagation phase, which is not addressed in this paper. This work compares the effectiveness of three contamination procedures for salt accumulation: P1) salt contamination by capillary absorption of salt solution, followed by drying; P2) continuous capillary absorption of salt solution; P3) placement of salt crystals on the surface of the materials followed by the conditioning of the specimens at high relative humidity until complete dissolution of the salts. The results of P1 and P2 procedures presented in this paper are detailed in a separate publication, while this paper focuses on P3 procedure and compares the results. The effectiveness of each procedure has been evaluated by assessing the salt distribution in the specimen using ion chromatography and scanning electron microscopy. The results show that P3 is technically the least complicated to set up and does not entail the risk of development of salt efflorescence or damage. However, it can lead to salt migration within the specimens to a greater depth, hence future research is proposed to counteract this effect.Heritage & Architectur
Proceedings of SWBSS 2021: Fifth International Conference on Salt Weathering of Buildings and Stone Sculptures
No full textHeritage & Technolog
A study on leaching of crystallisation inhibitor in mortars
No full textCrystallisation due to commonly occurring salts like sodium chloride (NaCl) is a known cause of damage in the built environment. Use of crystallisation inhibitors is a potential solution to reduce salt decay in building materials. Researchers have reported lower damage when sodium ferrocyanide (NaFeCN), a known NaCl crystallisation inhibitor, is mixed in fresh mortar. However, the high solubility of NaFeCN in water could make it susceptible to leaching and thus diminish its effect over time.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Heritage & ArchitectureMaterials and Environmen
A new accelerated laboratory test for the assessment of the durability of materials with respect to salt crystallization
No full textThe RILEM Technical Committee 271-ASC was set up in 2016 with the aim ofdeveloping an improved procedure for the assessment of the durability of porous building materials, such as brick and natural stone, against salt crystallization, accelerating the deterioration process without significantly altering its mechanism.The test procedure developed by the TC 271-ASC proposes a new approach to salt crystallization tests. It starts from the consideration that it is necessary to accumulate a certain amount of salt to activate the damage. Thus salt damage can be seen as a process developing in two phases: accumulation and propagation. Based on this approach, a new salt crystallization test procedure has been defined, consisting of two phases: a first phase, in which salts are introduced in the material and accumulate close to the evaporation surface, followed by a second phase, in which damage propagates because of repeated dissolution and crystallization cycles induced by re-wetting with liquid water and by relative humidity (RH) changes.In this paper the procedure is described and the reasons for the choices made are elucidated. The procedure has been tested on two types of limestone and, at the moment of writing, is being validated in a round robin test carried out on 9 different substrates and involving 11 laboratories. Based on the results of the round robin test, the procedure will be fine-tuned.Heritage & Technolog
Experimental Study on Properties of Hydraulic Mortars with Mixed in Crystallisation Inhibitors
No full textSodium chloride (NaCl) is one of the most commonly occurring weathering agents, responsible for a progressive damage in mortar. Current solutions to mitigate salt damage in mortar, such as the use of mixed-in water repellent additives, have often exhibited low compatibility with the existing building fabric. In the last years, research has shown promising results in mitigating salt decay by making use of crystallisation inhibitors. Sodium ferrocyanide is one of the inhibitors that has proven to be particularly effective to reduce damage due to sodium chloride crystallisation. In this research the possibility of developing hydraulic mortars with mixed-in inhibitor (sodium ferrocyanide) for an improved resistance to sodium chloride crystallisation damage is investigated. As a first step, the interaction between the inhibitor and the hydraulic binder: natural hydraulic lime (NHL), was studied; the results are presented in this paper. Various concentrations of sodium ferrocyanide were tested (0%, 0.1% and 1% by binder weight). The effect of the inhibitor on several physical (hydration, water absorption, pore size distribution) and mechanical (compressive and flexural strength) properties was experimentally assessed, using several complementary methods and techniques. The results show that the addition of the sodium ferrocyanide does not affect the fresh and hardened properties of mortar. These results are promising and open new possibilities for the application of inhibitors to improve the durability of hydraulic mortars.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Heritage & ArchitectureMaterials and Environmen
AeON - Interactive Robotic fabrication: Gesture Language to communicate with technology
No full textThis thesis is a inquiry into the idea of involving a human aspect in digital fabrication process, creating a poetic expression by developing a open dialogue between digital tools and the designers.Architecture, Urbanism and Building Science
Alkali silica reaction in the afsluitdijk: Assessment of concrete damage and remaining service life using experimental and modelling research
No full textAlkali Silica Reaction (ASR) is one of the degradation mechanisms in concrete that poses a threat to the service life of existing structures. This physio-chemical process is progressive and can affect the the strength, stiffness and stability of concrete structures. A lot of mitigation measures are available to prevent the deleterious effects of ASR in new structures. However, assessment and monitoring of ASR in the existing structures still remain a challenge. Thus the main aim of this thesis is to develop a simplified tool for the assessment of existing structures to assist the asset owners in decision making. This is addressed by a combination of petrographic techniques to quantify the damageand development of a numerical model to predict the remaining service life. Various existing petrographic tools (Damage rating index and image analysis) are investigated and modified to not only identify the ASR signs but also to quantify the damage. A meso-scale numerical model (ASR expansion model) is developed as an extension to the existing Delft Lattice Model to incorporate the effect of ASR by application of randomly distributed internal expansions. A case study (Afsuitdijk, The Netherlands) is used to apply these methods. The model is compared with the findings from the petrographic analysis using a physical parameter 'crack densities'. This model is able to simulate localised network of cracks typical of ASR and expansion strains as a function of time. These expansions are compared with the permissible expansion thresholds set byRILEM and CUR to assess the remaining service life. Additionally, the numerical model showcases the importance of different boundary conditions by making a comparative study between free expansions and concrete in confined state. Finally, the limitations and drawbacks of this expansion model are discussed critically.Civil Engineering | Structural Engineering | Concrete Structure
Justification and Excuse in the Criminal Law: Defences under the Indian Penal Code
No full textGeorge Fletcher\u27s theory, \u27Justification and Excuse in the Criminal Law\u27, has contributed to a deeper theoretical understanding of exculpatory defences in the discipline. It is a theory that not only has important practical implications for evidentiary issues related to criminal trials but also has a bearing on the very fulfilment of the objectives of criminal law. In this article, the author applies Fletcher\u27s theory to exculpatory defences under the Indian Penal Code and finds that it demonstrates an inadequate appreciation of the justification-excuse distinction. As a possible remedy, the author suggests certain amendments and additions to the Indian law pertaining to exculpatory defences in order to eliminate the inconsistencies resulting therefrom and making it theoretically defensible
